This invention relates generally to data transmission systems, and more particularly the invention relates to a burst demodulator for use in a high speed bidirectional digital transmission of voice, video, and data.
Much attention is being directed to converting any directional analog data transmission systems, such as the community antenna television (CATV) cable system into a more versatile bidirectional communication system. Today, over 60 million households in the United States enjoy the benefits of cable TV, virtually all of the information which travels into the home over the cable is in the form of analog television signals. Some subscribers now have the ability to send digital signals to select movies or provide other forms of low rate data information from the home to a central location. However, in the next few years the rate of digital information both entering and leaving the home over the CATV cable will increase dramatically. Equally, hybrid fiber/coax (HFC) plants are being installed for telephone/data outside the present CATV systems.
Disclosed in U.S. Pat. No. 5,553,064 by Paff et al. is a cable data transmission system which utilizes time division multiplexing in a downstream direction from a headend unit to multiple subscribers and a time division multiple access transmission from subscribers to the headend unit. The multiple upstream and downstream data channels are shared using different frequency bands. In the downstream, data are broadcast to all subscribers. However, each subscriber is assigned an identification number and a specific carrier frequency for receiving data. The bitstream is continuous using time division multiplexing (TDM) and frequency division duplex (FDD). In the upstream, subscribers send data to the headend in a burst fashion in assigned time slots using time division multiple access (TDMA). A quadrature phase shift keyed (QPSK) modulator is provided for data encoding and modulation for upstream and downstream transmission. In accordance with a feature of the invention claimed therein, a headend burst demodulator is provided for receiving data at the headend from subscribers. A Barker code is utilized in a preamble for data acquisition and synchronization of the data.
The present invention is directed to an improved data preamble and headend demodulator for use therewith which achieve closer spacing of data bursts along with burst acquisition and synchronization.